Tell her to leave you alone; if you like her back, don't drag your girlfriend along.
You can't make a girl jealous only when you know the girl likes the guy. If you know that the girl likes the guy but already has a girlfriend, then spend more time with the girlfriend that the guy already has and then laugh alot areound her and if the girl you're trying to get jealous treat her like a friend but ignore her, but not too harsh!
If he already has a girlfriend, likes this girl a lot, and they are comfortable together, then you should not be trying to get this guy away from her. It will only cause problems, mostly for you.
If he likes you better, then why does he even have a girlfriend?
Ask her to be your girlfriend.
You belong with Me by Taylor Swift
No way! As long as you and the other girl don't DO anything, it's not cheating, it's just part of being human. One reccomendation though- I wouldn't express your feelings for the other girl to your girlfriend. =)
Eat lots of cheese
She is your girlfriend which already suggests she likes you as well as you can tell by the way she makes you feel, talks to you, is around you and shows you in general.
She already said she likes you.
The one that likes you without a girlfriend.
That he likes you and want you to be his girlfriend.
you do what you think is right and your best option